1. Field of the Invention
The present invention relates generally to a tire pressure indicator adapted to monitor the condition of the tire pressure of a vehicle tire and, more particularly, to such a tire pressure indicator, which constantly monitors the condition of the tire pressure either when the car is running or stopped.
2. Description of the Related Art
The car driver may think that the engine is out of order if speed accelerating is slow and steering control requires much effort after having stepped the accelerator pedal. Actually, the problems may be caused due to insufficient tire pressure or deformation of the tires. If the tire pressure is excessively high, accelerating the speed becomes easy, however the car may vibrate heavily when running over an uneven road surface. Further, if the wheel diameters of the four tires of a car are not equal due to different tire pressures, the steering control of the car becomes difficult during a high speed running of the car, and a traffic accident may occur easily. Driving a car at a high speed when carrying a heavy load may cause the tires to explode if the tire pressure of each tire is insufficient or excessively high, and a catastrophe may follow.
According to a report on the analysis of traffic accidents during 1997˜1999 prepared by Ministry of Transportation in Taiwan, 0.6% of 8369 cases were resulted from falling or explosion of car tire that caused 48 persons to death and 75 persons injured. These accidents have a great concern with abnormal tire pressure. Therefore, it is important to check the pressure of the tires before driving the car.
Conventionally, a static tire pressure gage is used and connected to the air valve of the tire to check the pressure of the tire when the car stopped. According to this conventional method, it is not possible to monitor the pressure of each tire during running of the car. Therefore, car driver must have the habit of checking the pressure of each tire before driving the car. Forgetting to check the pressure of each tire before driving the car may easily lead to a traffic accident. There are known tire pressure indicators that use a radio transmitter and receiver system with tire pressure gages to monitor the pressure of each tire of the car. According to this design, a respective pressure sensor and a respective radio transmitter are installed in each tire, and a radio receiver and display unit is provided inside the car to receive radio signal obtained from the pressure sensor at each tire by the corresponding radio transmitter. The radio receiver and display unit demodulates received signal into a corresponding tire pressure signal and displays the tire pressure signal through a display thereof. This radio system incorporated tire pressure indicator is still not satisfactory in function due to the following drawbacks:    1. Because the pressure sensor and transmitter are installed inside the tire or the air valve of the tire and use battery power for operation (battery power is limited by size), it is inconvenient to frequently replace the battery when power low.    2. During high-speed running of the car, the internal temperature of the tire becomes high, and the high temperature may affect the stability and reliability of the battery and the related circuit, and an accident may occur if the battery fails.    3. There are suppliers who have the system to output a warning signal only when the tire pressure excessively high or low and not to produce any signal when the pressure of the tire is within a normal range. According to this design, the user cannot know if the system functions well or not.    4. Every tire of the car must be encoded or provided with a particular carrier channel to prevent interference when using radio to send tire pressure signal. This arrangement greatly complicates the circuit design and increases the manufacturing cost of the system.    5. Under the power-save mode, the battery lasts for only about 5˜6 months. It is complicated and expensive to frequently replace the battery.    6. A car tire is a rotor carrying a load for rotation at a high speed. However, adding tire pressure indicator parts to the tire changes the distribution of the mass of the tire. If the dynamic balance of the tire is not well controlled, the tire will vibrate severely during running. Leading to an explosion accident.    7. When replacing the tire or when the tire exploded, the pressure sensor and transmitter circuit of the tire pressure indicator may be damaged. Repair work and calibration of the pressure sensor and transmitter circuit is complicated and not easy.
Therefore, it is desirable to provide a tire pressure indicator that eliminates the aforesaid problems.